690 



DISSECTION OF THE LARYNX. 



an inch from the middle line ; as well as for a short distance into th( 

 inner surface of that cartilage. The muscle rests on the crico-thyroi 

 membrane, and is concealed by the sterno-thyroid muscle, 

 use. Action. It draws the cricoid cartilage upwards and backwards, 



as to increase the distance between the thyroid and the arytenoic 

 cartilages, and thus tighten the vocal cords. 



Posterior The POSTERIOR CRico-ARYTENOiD MUSCLE (fig. 244, c) arises from 

 arySnoid is tne depression by the side of the vertical ridge at the back of the 

 cricS? f c " co ^ cartilage. From this origin the fibres are directed outwards 

 cartilage: and upwards, converging to their insertion into the muscular proc 

 at the outer side of the base of the arytenoid cartilage. 



Kerato- 

 cricoid. 



Arytenoid 

 muscle lies 

 on back of 

 arytenoid 

 cartilages 



FIG. 244. HINDER VIEW OF THE 

 LARYNX. 



A. Aryteno-epiglottidean muscle. 



B. Arytenoid muscle. 



c.c. Posterior crico-arytenoicls. 



FIG. 245. SIDE VIEW OP THE 

 LARYNX. 



1. Crico-tbyroid muscle. 



2. Thyroid cartilage. 



3. Cricoid cartilage. 



Action. It draws the arytenoid cartilage downwards and outwards 

 to a slight extent, separating this from the one of the opposite side ; 

 but its principal action is to rotate the cartilage, turning outwards 

 the vocal process, and thus dilating the glottis. 



Kerato-cricoid muscle (Merkel). This is a small fleshy slip which 

 is occasionally seen at the lower border of the preceding muscle. 

 It arises from the cricoid cartilage, and is inserted into the back of 

 the lower cornu of the thyroid cartilage. 



The ARYTENOID MUSCLE (fig. 244, B) is single, and extends across 

 the middle line, closing the interval between the arytenoid cartilages 

 behind. Its transverse fibres are attached on each side to the outer 



